It is known that microporous adsorbents can be used to remove a contaminant from gas and liquids. However, adsorbents such as activated carbon become saturated with the contaminant and must be replaced by fresh adsorbents to maintain the desired performance of the filtration system. This can be costly and can be labor intensive in view of the environment in which filtering systems are often utilized. Furthermore, constantly replacing the adsorbent material can lead to human error wherein the adsorbent is still in service after its useful life.
In order to overcome the problems associated with changing out filters once the adsorbent becomes saturated, systems have been designed which utilize adsorbents that can be regenerated and reused. In general terms, there are two types of regenerable systems. The first is a pressure swing adsorption system and the other is a thermal (temperature) swing adsorption system. These systems allow a filter bed with an adsorbent material to be used over and over. In operation, a fluid is introduced into a filter bed wherein the adsorbent material removes a contaminant from the fluid. The filter bed includes sufficient amount of the adsorbent material to continue to remove the contaminant from the fluid stream for a designated period of time. At that point, the adsorbent material is at least partially saturated with the contaminant from the contaminated fluid stream. In order to remove the contaminant from the adsorbent material, a regeneration process is performed on the filter bed. As stated above, this can include pressure swing regeneration or temperature swing regeneration. However, during the regeneration process, the filter bed cannot be used to filter the contaminant from the fluid stream. Therefore, a second filter bed is usually provided, such that the second bed is in use when the first one is being regenerated and vice versa.
Temperature swing regeneration utilizes heat to remove the contaminant from the adsorbent material to allow the adsorbent material to be reused. There are many industries which utilize thermal or temperature swing adsorption processes. These applications include solvent recovery, air drying and removing contaminants such as CO2 and H2O from air prior to cryogenic separation. While temperature swing adsorption is an effective way to maintain the filters in a filter system, it can be expensive due to the high energy costs associated with producing the heat necessary to regenerate the filters.
Pressure swing adsorption (PSA) utilizes a pressurized regeneration gas that is introduced to the filter beds in a direction reverse to the flow of the higher pressure feed gas containing the contaminants. By passing low pressure gas in this reverse direction, the contaminants are removed from the adsorbent(s) so that the adsorbent(s) can be reused. As with the thermal swing adsorption system discussed above, the PSA system can also be expensive to operate due to the power consumption associated with pressurizing the feed gas, which typically necessitates a compressor and/or access to an industrial process which utilizes compressed gas. The items may not be conveniently available for certain applications. In addition, the purge gas requirements for PSA systems increase significantly as the adsorption isotherm for the given contaminants becomes more favorable. But favorable adsorption isotherms are needed to achieve high product purity with a reasonable volume of adsorbent. Therefore, achieving high purity product gas using PSA typically requires many beds and complicated cycles.
As is stated above, while use of a regenerable adsorbent can overcome some of the problems associated with replaceable adsorbents, the regeneration process necessitates the filter bed being at least partially pulled offline for the regeneration process. As a result, while the filter bed is being regenerated, the filtering system cannot process contaminated gas. This necessitates the system being shut down during the regeneration process. In order to overcome this problem, multiple filter beds have been utilized to allow one filter bed to be online and removing contaminants from the contaminated gas while the other filter bed is in a regeneration stage. While this overcomes the problems associated with shutting down the filter system for regeneration, it doesn't overcome the high energy requirements of the system. The energy requirements of the system is even a greater problem when the system is designed to remove more than one contaminant from the gas and/or when it is utilized at a remove location.
Accordingly, it has been considered desirable to develop a new and improved regenerable filter system which overcomes the foregoing difficulties and others and provides more advantageous results.